Search engines typically provide a source of indexed documents from the Internet (or an intranet) that can be rapidly scanned in response to a search query submitted by a user. As the number of documents accessible via the Internet grows, the number of documents that match a particular query may also increase. However, not every document matching the query is likely to be equally important from a user's perspective. A user may be overwhelmed by an enormous number of documents returned by a search engine, unless the documents are ordered based on their relevance to the user's query. One way to order documents is the PageRank algorithm more fully described in the article “The Anatomy of a Large-Scale Hypertextual Search Engine” by S. Brin and L. Page, 7th International World Wide Web Conference, Brisbane, Australia and U.S. Pat. No. 6,285,999, both of which are hereby incorporated by reference as background information.
Some queries by a computer user may concern continuing interests of the user. Some search engines, such as Google's Web Alerts, allow the user to explicitly specify such queries and receive alerts when a new web page in the top-ten search results appears for the query. However, it is too inconvenient for most users to explicitly register such queries. Google is a trademark of Google Inc. For example, in an internal study of 18 Google Search History users, out of 154 past queries that the users expressed a medium to strong interest in seeing further results, none of these queries was actually registered as a web alert. In addition, alerting the user to all changes to the search results for the query may cause too many uninteresting results to be shown to the user, due to minor changes in the web or spurious changes in the ranking algorithm.
Thus, it would be highly desirable to find ways to automatically identify queries in a user's search history that concern continuing interests of the user. In addition, it would be highly desirable to find ways to automatically identify user-relevant results to prior searches by the user that have not been shown to the user and to alert the user to such results.